Belt-mold forming apparatus grinding wheels

ABSTRACT

An abrasive molding material in granular form is drawn as a thin strip between a rotating core and an endless belt moving therearound and is thereby wound to be deposited as successive layers each of a thickness of from 0.5 to 3 mm on and around the core thereby to form a progressively molded and expanding grinding wheel, compression pressure being applied by rollers acting on the belt to this wheel. A desired density distribution in the wheel in the radial direction or in the axial direction can be obtained by varying the compression pressure progressively as the molding proceeds or by applying the compression pressure to a strip of a certain cross section by means of rollers of circular cylindrical shape of constant diameter.

United States Patent Hirosawa [451 Sept. 5, 1972 [54] BELT-MOLD FORMING APPARATUS GRINDING WHEELS [72] Inventor: Norlo Hirosawa, Hiroshima, Japan [73] Assignee: Kuretolshi Kabushiki Kaisha,

Hiroshima-Ken, Japan [22] Filed: April 28,1971

211 Appl.No.: 138,171

[52] C1. ..425/363, 425/373, 51/293 [51] Int. Cl. ..B30b 5/00, 1330b 9/28 [58] Field of Search ..425/363, 365, 368, 373

[56] References Cited UNITED STATES PATENTS 3,241,182 3/1966 Y Kessler ..425/373X 3,400,196 9/1968 LeRoy ..425/373X FOREIGN PATENTS OR APPLICATIONS 574,528 4/1959 Canada. ..425/363 Primary Examiner-J. Howard Flint, Jr. AttameyWenderoth, Lind & Ponack ABSTRACT An abrasive molding material in granular form is drawn as a thin strip between a rotating core and an endless belt moving therearound and is thereby wound to be deposited as successive layers each of a thickness of from 0.5 to 3 mm on and around the core thereby to form a progressively molded and expanding grinding wheel, compression pressure being applied by rollers acting on the belt to this wheel. A desired density distribution in the wheel in the radial direction or in the axial direction can be obtained by varying the compression pressure progressively as the molding proceeds or by applying the compression pressure to a strip of a certain cross section by means of rollers of circular cylindrical shape of constant diameter.

N0 Claims, 18 Drawing Figures PATENTED 1 2 3.889.187 sum 1 or 3 FIG.I

NORIO EIROSAWA,

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NORIO HIROSAWA,

INVENTOR BELT-MOLD FORMING APPARATUS GRINDING WHEELS BACKGROUND OF THE INVENTION This invention relates generally to abrasive grinding wheels and more particularly to an apparatus for forming abrasive materials into artificial or manufactured, abrasive grinding wheels having the shapes of cylinders by a new belt-mold technique.

In general, grinding wheels are rotated at high peripheral speeds of the order of from 1,000 to 5,000 meters per minute in grinding various work materials. For this reason, if there is substantial unbalance in a grinding wheel itself, due to irregularities or deviations in the density thereof, an impact effect due to centrifugal force will develop and give rise to machine vibration, which will cause difficulty in precision grinding and, in the worst case, breakage of the wheel.

In precision grinding with a grinding wheel, when voids between cutting peaks due to loss or absence of abrasive particles or irregularities in particle holding force occur, the work material is severely scratched-or scored. In the case of a cylindrical workpiece, the resulting vibration causes the workpiece to be ground into a structure of polygonal cross section, whereby it becomes difficult to obtain the required degree of roundness. Furthermore, the rate of wear of the grinding wheel increases.

As a large grinding wheel of an outer diameter of 900 mm, a thickness of 100 mm, and a central hole diameter of 300 mm, for example, for use in a roll grinding machine for grinding rolls becomes worn, its outer diameter and peripheral speed decrease, whereby the grinding conditions vary. The contact area between the grinding wheel and the workpiece (roll) becomes smaller as the outer diameter of the grinding wheel decreases, and the peripheral speed also decreases. For this reason, if the grinding operation is continued under in a similar manner, the load on each abrasive grain will increase, whereby the rate of wear of the wheel will increase, and the grinding efficiency and work efficiency will drop.

In almost all modern grinding machines, means are provided for varying the peripheral speed of the grinding wheel, the peripheral speed of the workpiece being ground, and the wheel load and these variables are effectively varied by the operator as necessary. The grinding efficiency could be increased even further, of course, if it were possible to use grinding wheels each having a density distribution such that the density increased progressively from the outer periphery toward the central part of the wheel.

Among the methods generally used heretofore the forming grinding wheels, there are the pour-casting method in cases where the starting materials are mixtures of pasty or liquid form and principally the mechanical pressing method in cases where the starting materials are in powdery and granular form.

By the pour-casting method, occurrance of density irregularities due to differences in the specific gravities of the starting materials cannot be avoided. On the other hand, by the mechanical pressing method, density irregularities tend to be caused by nonuniform internal stress which occurs at the time of compression, this tendency becoming pronounced particularly when the density of the grinding wheel becomes high. For this reason, the grinding wheel easily develops cracks when I it is being taken out of the die or mold. Furthermore, it is very difficult, by these methods, to produce in a consistent and stable manner grinding wheels whichto the radial require density adjustments with respect and thickness or axial directions.

SUMMARY OF INVENTION It is an object of this invention to provide an apparatus whereby excellent grinding wheels having im- 1 there are provided an apparatus for forming grinding wheels in which an abrasive material isfed as a thin continuous strip toward a rotor core being rotated by a moving belt disposed therearound, the strip thereby being drawn between the belt and rotor core in a winding manner to deposit successive layers of the strip on and around the core and thereby to form a progressively molded and expanding grinding wheel structure, and compression pressure is applied on this structure.

The nature, principle, and utility of this invention will be more clearly apparent from the following detailed description when read in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an elevation, herein considered as a side elevation, showing the essential parts of one example of an apparatus constituting a preferred embodiment of this invention;

FIG. 2 isv a relatively enlarged, fragmentary, end elevation, partly in vertical section, showing certain essential parts of the apparatus shown in FIG. 1;

FIG. 3 is a section taken along the plane indicated by line Ill-III in FIG. 2 as viewed in the arrow direction;

FIG. 4 is a section similar to FIG. 3 showing the state of the apparatus immediately prior to the start of wheel-forming operation;

FIGS. 5, 6, and 7 are cross sections each taken along a plane as indicated by line V-Vll in FIG. 2 and as viewed in the arrow direction and showing the cross section of the molding material being fed through a feeding nozzle from a hopper;

FIGS. 8, 10, and 12 are cross sectional views showing molded grinding wheels formed in accordance with this invention by using feeding nozzles of the cross sections indicated in FIGS. 5, 6, and 7, respectively;

FIGS. 9, l1, and 13 are planar views showing halves of the grinding wheels shown in FIGS. 8, l0, and 12, respectively;

FIGS. 14 and 16 are cross sectional views and FIGS. 15 and 17 are corresponding planar views showing spindle work mounted on a rotating magnetic chuck.

DETAILED DESCRIPTION An important feature of the wheel-forming technique according to this invention isthat differences in density of the wheels due to internal stress distributions which occur at the time of compression forming are reduced to extremely small values, and, for this reason, by carrying out the forming with a wrapping and laminating procedure with successive thin layers of the molding materials of thicknesses of, for example, of from 0.5 to 3 mm, it is possible to produce grinding wheels of extremely small density deviations, which was very difficult to attain by prior art techniques.

Another important feature of the technique according to this invention is that the density of a wheel can be caused to assume any desired distribution. For example, when ,a certain density gradient in the .radial direction is required, it can be readily established by controllably varying the pressure exerted on the wheel during its laminar forming process. When a certain density gradient in the thickness direction is required, it can be easily attained by suitably selecting the cross sectional shape of the material feeding nozzle for smoothing at the end of hopper and shaping the material as a strip from a hopper to the entrance of the belt mold.

These and other features and details of this invention will become apparent from the following detailed description with respect to a preferred embodiment of the invention.

Referring first to FIGS. 1 through 4, the apparatus shown therein has a frame 1 supporting the various components thereof and provided with vertical frame bearing supports la rotatably supporting a rotary spool 2. The rotary spool comprises a rotor core 3 with integrally-formed shaft ends 3a extending coaxially therefrom and side disk flanges 4 fixed coaxially to respective ends of the core 3, the lateral spacing between the flanges 4 being adjusted to suit the width of a belt 5 passed around the core 3 and between the flanges 4. The axis of the spool 2 is directed horizontally and laterally (left and right as viewed in FIG. 2), the shaft ends 3a being rotatably supported in split type bearings 22 mounted on the bearing supports la.

The belt 5, which is an endless type, is retained closely wrapped-around the core 3 by a combination of mechanisms including small wrapping rollers 6 disposed in symmetrically opposed positions on respective sides of the central vertical plane passing through the axis of the core 3 and pressed toward the core and against the outer surface of the belt 5 by respective hydraulic devices 7 exerting force on the rollers 6 through symmetrical mechanisms including arms 11 of levers. The belt 5 is maintained in a tensioned state by a hydraulic device 8 operating by way of a movable pulley carriage l8 and an idler pulley supported thereon as described hereinafter.

Thus, the rotor core 3 and the inner surfaces of the side flanges 4 of the rotary spool 2 and the inner sur-' face of the belt 5 in its part encompassing the rotor core 3 define and form the cavity of a rotary belt mold of expandable outer peripheral dimension.

Pressure rollers 9 of relatively large diameter in symmetrically opposed position on respective sides of the above mentioned central vertical plane are pressed by'a hydraulic device 10 toward the core 3 and against the outer surface of the belt 5 at a height level below the small rollers 6. The rollers 6 are rotatably supported on the ends of arm 11 which ends have two pawls, and the width between the pawls is preferably of minimum dimensions allowable as determined by stress analysis.-

Above the rotary mold, the belt 5 is passed around a friction drive pulley 13 coupled to a motor 12 for receiving driving power therefrom .and rotatably supported on the frame 1 and around an idler pulley rotatably mounted on the aforementioned movable pulley carriage l8 slidably mounted on the frame 1. The belt 5 is thus driven -in the arrow direction, whereby the rotary spool 2, wrapping rollers 6, and pressure rollers 9 are rotated by frictionaldrive due to their contact with the belt.

A hopper '14 for supplying the granular material 15 to be molded by the rotary, mold 2 is suspended thereabove andhas a feeding nozzle 14a extending downward from the bottom of the hopper and has an exit opening having a slot shape with a relatively long dimension in the direction parallel to the axis of the rotary spool 2. The hopper 14 is'adapted to be controllably movable, together with the nozzle l4a,in the vertical direction by a hopper height controlling cam device 16.

The belt 5 is a flat type with a rectangular cross section and is'made of a rubber, synthetic resin, metal, fabric, leather, or some other suitable materiaL-The belt must fulfil the requirements of (l) a tensile strength of at least the order of I00 kg/cm '(2) a minimum radius of bend of 20 mm in a bend test, (3) a high coefficient of friction, (4) a surface of fine texture and smoothness, and (5) capability of fulfilling the above requirements under repeated use.

The abrasive material to be molded must be in a form which has high fluidity in free flow and is readily agglomerated into a molded structure. These requirements are amply met by mixed abrasive materials ordinarily used for grinding wheels.

The above mentioned hydraulic devices 7, 8 and 10 are all connected to and coordinatedly controlled by a controller 23.

The belt-mold apparatus of the above described organization according to this invention operates in the following manner.

First, the motor 12 is started to drive the belt 5 and thereby to start the rotation of the rotary mold. Then a specific quantity of the granular, abrasive molding material 15 is placedin the hopper 14, which is then raised by the hopper height controlling cam device 16 at a rate such that a continuous strip of the molding material of a thickness of from 0.5 to 3 mm is extruded through the feeding nozzle 14a and deposited as a winding of successive layers on the core 3.

Thus, feeding of the molding material and pressure molding are carried out in a continuous manner, whereby the diameter of the molded grinding wheel 17 progressively increases. Accordingly, the movable pulley carriage 18 progressively moves in the arrow direction of FIG. 1, while the wrapping rollers 6, the arms 11, and the pressure rollers 9 also retract while maintaining their respective set pressing forces toward the belt 5.

The molding speed can be controllably adjusted by adjusting the rotational speed of the rotary mold 2 and the distance through which the hopper 14 is raised per revolution of the rotary mold 2.

The molded density can be controllably adjusted principally by adjusting the pressing force of the pressure rollers 9. Accordingly, by progressively varying this pressing force the density can be caused to vary from the central part of the wheel toward the outer periphery thereof. For example, I have found that the density can be caused to decrease progressively from the inner rim toward the outer periphery of a wheel as shown in FIG. 14 and 15 by progressively reducing the pressing force, or the density can be caused to increase progressively from the inner rim toward the periphery as shown in FIGS. 16 and 17 by progressively increasing the pressing force.

In another mode of density distribution according to this invention, the density of a wheel is caused to have a gradient in the thickness direction thereof by using a material feeding nozzle 14a of a crosssection such as to produce the desired density distribution. More specifically, for example, by using a nozzle 14a such as to feed the molding material in the form of a strip or layer with a cross section as shown in FIG. 5, and then molding this material with pressure rollers 9 in the shape of circular cylinders of constant diameter, it is possible to produce a grinding wheel of relatively high density in its flank side regions and of relatively low density in its central region as indicated in FIGS. 8 and 9.

By using a nozzle 140 such as to feed the material with a cross section as shown in FIG. 6 and then molding this material with constant-diameter cylinder type pressure rollers 9, a grinding wheel with a relatively higher density in the central region and relatively lower density in its flank regions as indicated in FIGS. and 11 can be produced. With a material layer feeding shape of uniform thickness as shown in FIG. 7 and the use of constant-diameter cylinder type rollers 9, a grinding wheel of uniform density in its thickness direction is produced.

Thus, this invention provides a molding apparatus whereby grinding wheels without density irregularities or with controlled density distributions can be produced. When a wheel of this character is rotated at high speed, it is under dynamic balance as a rotating body even from a theoretical viewpoint, and impact irregularities due to centrifugal force are effectively prevented.

I have found that a grinding wheel in which the density is caused to decrease progressively from the center toward the outer periphery as indicated in FIGS. 14 and is also effective for improving providing the grinding efficiency in roll-grinding operations. Furthermore, since a cylindrical grinding wheel is ordinarily used in the manner indicated in FIG. 18, it is preferably fabricated to have a uniform density as indicated in FIGS. 12 and 13, whereby the advantage of stable grinding operation from beginning to completion can be attained. FIG. 18 illustrates the case wherein workpieces 20 mounted on a magnetic chuck 21 are being ground by a cylindrical type grinding wheel 19 mounted on a vertical spindle.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention but is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from" the spirit and scope of the invention. For example, while only two pressure rollers 9 are used in the above described example, it will be apparent that more than two pressure rollers can be used to apply compression pressure to the material being molded. These rollers may be adapted to rotate and function independently, or they may be intercoupled with an endless belt thereby to form a pressure-applying device in the form of a caterpillar.

As another example, while an endless belt 5 is used in the above described example, it is alternatively possible to use a belt of'limited but ample length alternately wound. and unwound on two reels each time a grinding wheel is formed, between which reels the rotary mold is positioned. As a further example, the wrapping rollers 6, pressure rollers, and the carriage 18 need not be actuated by hydraulic means but can be actuated by electrical or mechanical means.

Iclaim:

1. Apparatus for forming grinding wheels comprisa rotary spool (2) rotatably supported and comprising two side flanges (4) and a rotor core (3) interposed coaxially therebetween;

a movable belt (5) having a part retained to encompass the rotor core, except for a small sector thereof, between the two side flanges with minimal clearance between the belt and the flanges; said rotor core, flanges, and belt thereby forming a rotary mold of expandable outer dimension;

retaining means (6, 11, 7) retaining said part of the belt and adapted to apply controlled retaining force thereon while retracting to compensate for expansion of the rotary mold;

means (12, 13, 18, 8) for controllably driving, guiding, and tensioning the belt to cause the same to move in one longitudinal direction thereof and rotate the rotary spool;

feeding means (14,14a, 16) including a feeding nozzle (14a) for feeding an abrasive material as a thin continuous strip through said nozzle toward the rotating rotor core at said small sector, said strip thereby being drawn between the belt and rotor core in a continuous winding manner to be deposited as successive layers on and around the core and thereby to form a progressively molded and expanding structure (17) of a grinding wheel, the feeding nozzle being adapted to retract away from the rotor core to compensate for the expansion of the grinding wheel structure; pressure means (9,10) adapted to apply controlled pressure on said belt part thereby to impart controlled compression pressure to the expanding structure, in conjunction with the belt and retaining means, while retracting away from the rotor core to compensate for the expansion of the structure; and

control means (23) connected to said retaining means, means for tensioning the belt, and pressure means for coordinated control thereof.

2. Apparatus for forming grinding wheels according to claim 1 in which:

said belt is an endless belt;

said driving, guiding, and tensioning means comprises an electric motor (12), a driving pulley (l3) driven by the motor, an idler pulley, the belt being passed around the driving and idler pulleys, a slidably supported carriage (l8) rotatably supporting the idler pulley, and first actuating means (8) connected to the carriage for applying controlled tension by way of the carriage and idler pulley to the belt;

said retaining means comprises at least two wrapping rollers (6) disposed symmetrically and closely to each other on respectively opposite sides of the feeding nozzle and contacting the outer surface of the belt, a member (1 l) rotatably supporting each wrapping roller and adapted to move the roller toward and away from the rotor core, and second actuating means (7) connected to said member for applying controlled force and movement by way of the member to the roller; and

said pressure means comprises at least two pressure rollers (9) disposed on respectively opposite sides of the rotor core and contacting the outersurface of the belt at said belt part, support members rotatably supporting the pressure rollers and adapted to move the rollers toward and away from the rotor core, and third actuating means connected to said supporting members for applying force and movement by way of the members to the pressure rollers;

said first, second, and third actuating means being connected to and controlled by the control means.

* III I I 

1. Apparatus for forming grinding wheels comprising: a rotary spool (2) rotatably supported and comprising two side flanges (4) and a rotor core (3) interposed coaxially therebetween; a movable belt (5) having a part retained to encompass the rotor core, except for a small sector thereof, between the two side flanges with minimal clearance between the belt and the flanges; said rotor core, flanges, and belt thereby forming a rotary mold of expandable outer dimension; retaining means (6, 11, 7) retaining said part of the belt and adapted to apply controlled retaining force thereon while retracting to compensate for expansion of the rotary mold; means (12, 13, 18, 8) for controllably driving, guiding, and tensioning the belt to cause the same to move in one longitudinal direction thereof and rotate the rotary spool; feeding means (14,14a, 16) including a feeding nozzle (14a) for feeding an abrasive material as a thin continuous strip through said nozzle toward the rotating rotor core at said small sector, said strip thereby being drawn between the belt and rotor core in a continuous winding manner to be deposited as successive layers on and around the core and thereby to form a progressively molded and expanding structure (17) of a grinding wheel, the feeding nozzle being adapted to retract away from the rotor core to compensate for the expansion of the grinding wheel structure; pressure means (9,10) adapted to apply controlled pressure on said belt part thereby to impart controlled compression pressure to the expanding structure, in conjunction with the belt and retaining means, while retracting away from the rotor core to compensate for the expansion of the structure; and control means (23) connected to said retaining means, means for tensioning the belt, and pressure means for coordinated control thereof.
 2. Apparatus for forming grinding wheels according to claim 1 in which: said belt is an endless belt; said driving, guiding, and tensioning means comprises an electric motor (12), a driving pulley (13) driven by the motor, an idler pulley, the belt being passed around the driving and idler pulleys, a slidably supported carriage (18) rotatably supporting the idler pulley, and first actuating means (8) connected to the carriage for applying controlled tension by way of the carriage and idler pulley to the belt; said retaining means comprises at least two wrapping rollers (6) disposed symmetrically and closely to each other on respectively opposite sides of the feeding nozzle and contacting the outer surface of the belt, a member (11) rotatably supporting each wrapping roller and adapted to move the roller toward and away from the rotor core, and second actuating means (7) connected to said member for applying controlled force and movement by way of the member to the roller; and said pressure means comprises at least two pressure rollers (9) disposed on respectively opposite sides of the rotor core and contacting the outer surface of the belt at said belt part, support members rotatably supporting the pressure rollers and adapted to move the rollers toward and away from the rotor core, and third actuating means connected to said supporting members for applying force and movement by way of the members to the pressure rollers; said first, second, and third actuating means being connected to and controlled by the control means. 